1. Field of the Invention
The present invention relates to testing electronic circuits in general, and in particular to testing electronic circuit based upon JTAG standard specified by IEEE 1149.1 specification.
2. Related Art
The use of the IEEE 1149.1 JTAG interface to communicate with a processor under test on a circuit board is well known in the prior art. There is a wide range of operating voltages for the target microprocessor and the circuit boards. As a consequence, the JTAG interface must be able to adjust its operating voltage to be compatible with the target system. If the operating voltage is set incorrectly this could result in damage to the system (microprocessor and circuit) under test.
One obvious solution would be to set the operating voltage manually. This is usually done with the user issuing a command to the probe to set the operating voltage to a level compatible with the target. This solution introduces the possibility that the user may specify the wrong value to the test software which results in the wrong voltage level being used thereby causing physical damage to the processor and other circuit components. To minimize this human error a more efficient method and apparatus are required for setting the JTAG interface between the probe and unit under test.